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THE ACID  OPEN-HEAETH  PROCESS.                        187
consequent long exposure to the flame,, will result in a thorough, washing of the bath. I believe that there is a limit to this action, and that little can be gained by raising the content of carbon in the melted bath above 1 per cent., for this proportion insures a vigorous boil. It is difficult to see how the condition of the bath, after it has been run down from 1 per cent, of carbon to three-tenths of 1 per cent., can be different from the condition which would have existed if the original content had been 2 per cent. It seems probable that one or two hours of exposure of the completely liquid bath to the flame would give ample opportunity for any reactions which could be in progress.
SEC. Xh.—Sulphur and phosphorus.—In the above records no account is taken of sulphur or phosphorus, but experience proves that the content of phosphorus in the steel will be determined by the initial content in the charge. It is true that acid open-hearth slag may contain some phosphorus, and I have found one case where it held 0.04- per cent., but it would require a higher percentage than this to make a difference in the metal that could be detected by ordinary analysis, so that it must be assumed that every molecule of phosphorus in the pig-iron, scrap and ore will appear in the finished metal.
The percentage of sulphur cannot be predicted with precision. Traces of this element may be burned during melting and pass away as sulphurous anhydride, but the proportion eliminated is small. On the other hand, there is a tendency to absorb sulphur from the flame, and with bad coal, and especially when the slow working of the furnace renders it necessary to expose the charge to the gases for a long time, the amount thus absorbed may be ruinous. It has been suggested that the addition of lime in the producer might retain at least a part of the sulphur in the ashes of the producer, but it would give trquble by making a fusible ash. The ore is also a source of contamination, for it generally contains pyrites. As the ore floats on the bath some sulphur may be oxidized above the surface and the products pass away with the flame, but the remainder will be absorbed by the bath.
SEC. Xi.—Tests.—The condition and nature of the metal and slag are determined by taking samples from the furnace by means of a small, ladle and casting test-ingots with a cross-section about one inch square. These are chilled in water and broken, and the